Email API for developers building AI agents

What the email API does

An email workflow must know which message a customer replied to. It must know if an address bounced. It must know if a new send repeats an earlier message.

The Hail email API has inbound messages, attachments, and delivery events. Use it from your server, through the CLI, or as an MCP tool in your agent.

• Send plain-text or HTML email, with optional attachments.
• Use a verified custom domain or a Hail-hosted sending address.
• Receive inbound email and inspect messages through the API.
• Follow delivery, bounce, and complaint events. HTML messages can also produce open and click events.

Start with one email to your own inbox. Then connect the events your application needs. A sent status does not establish inbox placement or prove that a person read the message.

How long does email domain warmup take?

There is no fixed number of weeks that makes a new domain ready. Start with a small, consistent volume of wanted mail. Increase it as delivery results and recipient responses support it; slow down when bounces, complaints, or deferrals rise.

Domain reputation, sending-IP reputation, DNS setup, and provider approval are separate concerns. A verified domain has passed a setup check. It has not earned a guarantee that every message will reach an inbox.

Google's sender guidelines recommend increasing volume gradually and monitoring server responses and spam rates. Use those signals rather than a calendar deadline.

Check authentication before increasing volume

SPF authorizes sending servers for the envelope domain. DKIM signs messages. DMARC checks whether a passing SPF or DKIM result aligns with the visible From domain, and publishes your requested policy for failures.

Use the email deliverability checker to inspect your DNS, then read the DMARC policy guide. DNS checks alone cannot tell you which folder received a message.

Self-hosting with Amazon SES

SES sandbox access and domain warmup are different steps. Moving out of the sandbox requires a production-access request in the AWS Region you use. Describe your sending use case and how you handle bounces and complaints. Follow Amazon's production-access instructions for the current process.

Use email with SMS and voice

Use email for the details a person needs to keep, SMS for a short update, and the voice API when the task needs a conversation. Hail's usage-based pricing covers all three channels.